main(List<String> args) {
  Person p = Person();
  print(p.toString());
  print(p.hashCode);

  final map = {"name": "why", "age": 18, "height": 1.88};
  print(map.runtimeType);
  Map<String, dynamic> map1 = {"name": "why", "age": 18, "height": 1.88};
  Map<String, Object> map2 = {"name": "why", "age": 18, "height": 1.88};
}

//Dart中，所有类都继承自Object
class Person {}
